The paper discusses the operational space of the flat-top plasma in the Spherical Tokamak for Energy Production (STEP) power plant, which is designed to demonstrate net electric power production. The integrated modelling workflow, including core plasma modelling, MHD stability analysis, SOL and pedestal modelling, coil set and free boundary equilibrium solvers, and whole plant design, is described to optimize fusion performance while satisfying various physics and engineering constraints. The JETTO core plasma model is used to develop individual flat-top operating points that meet the criteria for fusion power performance within operational constraints. Key plasma parameters such as normalized beta, Greenwald density fraction, auxiliary power, and radiated power are scanned to explore the operational space and derive candidate non-inductive flat-top points. Two auxiliary heating and current drive systems are considered: electron cyclotron systems only or a combination of electron cyclotron and electron Bernstein waves. The assumed auxiliary heating and current drive methods result in two candidate flat-top points for each system, totaling four operating points. Lower confinement assumptions suggest operating points in high-density, high auxiliary power regimes, while higher confinement allows access to a broader parameter regime in density and power while maintaining target fusion power performance. The paper also discusses the assumptions and constraints for the STEP flat-top, including geometry, magnetic field, fusion power, EC and EBW access, MHD instabilities, plasma current, energy confinement, power losses, and detachment access. The operational limits considered for the parameter scans include fusion power, Q-factor, plasma current, MHD stability, and confinement factor. The integrated core plasma modelling with JETTO is described, and scan templates based on electron cyclotron and electron Bernstein wave systems are presented. The paper concludes with a summary of the main conclusions and the operational space exploration.The paper discusses the operational space of the flat-top plasma in the Spherical Tokamak for Energy Production (STEP) power plant, which is designed to demonstrate net electric power production. The integrated modelling workflow, including core plasma modelling, MHD stability analysis, SOL and pedestal modelling, coil set and free boundary equilibrium solvers, and whole plant design, is described to optimize fusion performance while satisfying various physics and engineering constraints. The JETTO core plasma model is used to develop individual flat-top operating points that meet the criteria for fusion power performance within operational constraints. Key plasma parameters such as normalized beta, Greenwald density fraction, auxiliary power, and radiated power are scanned to explore the operational space and derive candidate non-inductive flat-top points. Two auxiliary heating and current drive systems are considered: electron cyclotron systems only or a combination of electron cyclotron and electron Bernstein waves. The assumed auxiliary heating and current drive methods result in two candidate flat-top points for each system, totaling four operating points. Lower confinement assumptions suggest operating points in high-density, high auxiliary power regimes, while higher confinement allows access to a broader parameter regime in density and power while maintaining target fusion power performance. The paper also discusses the assumptions and constraints for the STEP flat-top, including geometry, magnetic field, fusion power, EC and EBW access, MHD instabilities, plasma current, energy confinement, power losses, and detachment access. The operational limits considered for the parameter scans include fusion power, Q-factor, plasma current, MHD stability, and confinement factor. The integrated core plasma modelling with JETTO is described, and scan templates based on electron cyclotron and electron Bernstein wave systems are presented. The paper concludes with a summary of the main conclusions and the operational space exploration.